1. Field of the Invention
The present invention relates generally to artificial speech aids, and in particular to the means for tone generation used therein.
2. Description of the Prior Art
Artificial speech aids enable individuals that have lost the use of their vocal cords to speak. These devices function to produce a substitute vocal sound that, when delivered to the user's oral cavity, can be articulated into words in the normal manner. Artificial speech devices essentially consist of a means for generating a tone, and a means for delivering that tone to the user's oral cavity.
Present art speech devices generate the substitute vocal sound either electrically or pneumatically. An electrically operated tone generating means typically produces sound by vibrating a diaphragm electromagnetically to a suitable frequency. For an example of an electrically operated tone generator, see U.S. Pat. No. 3,066,186 to Trammel. In a pneumatic device, pressurized air flows through the tone generating means, vibrating a reed or diaphragm contained therein, thereby producing the artificial speech sound. For an example of a pneumatically operated tone generating means, see U.S. Pat. No. 4,223,411 to Schoendorfer et al.
The tone delivery means, in general terms, is a conduit, connected to the tone generating means, through which the tone is propagated and thereby delivered to the user's oral cavity. A common tone delivery means is the intra-oral tube, which is simply a hollow, flexible, plastic tube which delivers the tone through insertion directly into the user's mouth. Another delivery means consists of a small diameter plastic tube that is nasally inserted, and through which the 5 tone is delivered to the user's oral cavity. For individuals that have a stoma or opening in their throat, as results from a tracheostomy, suitable conduit means exist for delivery of the tone through the stoma, and into, and up the trachea, to the oral cavity.
Electrically operated artificial speech aids have the advantage of being small in size, and are generally battery operated and thus portable. However, the sound energy produced by current art electrically operated tone generators dissipates quickly. Therefore, to insure the delivery of a tone of sufficient volume to produce audible speech, the tone must be delivered directly into the user's oral cavity. This restriction generally requires the use of an intra-oral tube, as described previously. Use of an intra-oral tube, however, requires the presence of the tube in the user's mouth during speech, which presents articulation problems for certain word sounds and can become a nuisance to the user when held in the mouth overprolonged periods of time. Furthermore, an intra-oral tube requires a free hand or support means to position it properly in the user's mouth. Many individuals that can benefit from the use of an artificial speech aid are not physically capable of holding a tone delivery means, and use of a support device can burden the user with additional unnatural apparatus.
Pneumatic tone generators have the advantage of being compatible with a wider range of tone delivery means than electronic tone generators. The pressurized air which vibrates the sound producing mechanisms also acts to amplify and "carry" the tone, thereby enhancing the tone delivery capacity of the particular delivery means. For example, a pnuematic tone generator can be used with a nasally inserted delivery means, which delivery means is longer than an intra-oral tube, as a nasally inserted delivery means must be able to reach from the exterior of the user's nasal pharynx to the posterior oral pharynx, to provide for tone delivery. Thus, due to its length, a nasal tube delivery means does not provide an adequate acoustic conduit for the propagation of the lower volume sound associated with an electronically produced tone, as such tone would quickly dissipate and would not provide for audible speech without the sound enhancement provided by a pressurized air flow. In addition, a pneumatic speech system that includes a nasal delivery means eliminates the articulation and nuisance problems associated with intra-oral tube systems, and eliminates the necessity for a free hand or support device to hold the delivery means.
Another advantage of a pressurized air flow concerns the fact that various tone delivery means can become blocked with mucous or saliva and rendered ineffective, whereas an air flow passing through the particular delivery means can prevent this clogging. However, a disadvantage of pneumatic tone generators lies in the fact that the air flow needed to vibrate the sound producing mechanism can be of such a volume so as to cause excessive drying of the moist tissue of the oral cavity surrounding the point of exit of the air from the tone delivery means, and also may result in air swallowing and stomach distention. This drying can necessitate periodic removal or disuse of the tone delivery means.